This project investigates the relationship between pregnancy and migrainous headache based on the data recorded from a large group of women in pregnancy -- the Collaborative Perinatal Project gravida. Subgroups of pregnant women characterized by the absence and presence of migraine and other recurrent headaches prior to or during pregnancy will be identified. Characteristics of these subgroups will be described and compared on a variety of demographic, sociological, medical and gynaecological factors, and the associations of headache with other diseases. The subgroup of women who have a past history of migraine, but who reported absence of headache during their pregnancy will be studied.